A test for comparing the means of two samples, or the mean of one sample (or even parameter estimates) with a specified value; also known as the "Student t-test" after the pseudonym of its inventor.

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1answer
11 views

Pre-post analysis with multiple post measures

I am having trouble deciding what type of analysis to use for the following data: I have two groups (one control, one treatment) and took a pre-measure of my dependent variable, and then 3 ...
0
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0answers
16 views

Significance of linear combination of two insignificant regression parameters

I'm running a model with an interaction term, of the general form: $Y=b_1X_1+b_2X_2+b_3X_1X_2$, whereby $X_2$ is a dummy variable and $X_1$ is continuous. Neither $X_1$ nor $X_2$ turn out as ...
0
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0answers
13 views

What statistical test to use for A/B testing

I'm trying to understand how A/B testing works for a simple 2x2 contingency table. I have found two different types of solutions: 1) Calculate an aggregate probability of conversion assuming that ...
2
votes
1answer
31 views

one sample $t$-test with range values

I need to compare an average value for an experimental group ($n=5$) with a reference value given by legislation. But this reference value in given as [min - max] range. I have to compare my ...
0
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1answer
30 views

Reproducing simple t-test result with ANOVA

We know that a t-test is just a special case of ANOVA, so I tried to reproduce the result of the following t-test with aov() or ...
0
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1answer
26 views

Random variable variance

I have the model $y_i=\beta_1+\beta_2 X_i+ u_i$ where $u_i\sim\text{iid } N(0,\sigma^2)$. I estimate $\beta_1$ and $\beta_2$ by drawing a straight line between the first $(x_1,y_1)$ and last dot ...
2
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1answer
27 views

wilcox.test usage in R

I would like to know if there is a difference in the values taken from measurements of a given characteristic sampled at primary forest (Point=1) and secondary ...
0
votes
1answer
31 views

Is Student's $t$-test the right choice?

I have 2 patient populations taken from the same time period that underwent 2 different surgical laparoscopic procedures. I want to compare the rate of conversion to an open surgical procedure. In my ...
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0answers
10 views

Mixed model approach to one sample tests

Is it possible to use the mixed-models approach to test if the mean of a sample is significantly different from zero? I know that mixed models, with crossed random effect for target, and subject, are ...
3
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2answers
111 views

Mann Whitney test with unequal variances [duplicate]

I am confused on what I have read about the Mann whitney test. We are testing whether our actual data is the same as our projected data. We had been using the t-test until we realized the data might ...
-2
votes
1answer
32 views

Which statistical test is appropriate for determining whether there is a significant difference in the exam scores of 2 groups(abnormal distrib)?

Male exam scores 58 54 61 64 60 60 45 44 53 54 32 56 43 69 69 72 66 45 63 49 48 53 Female exam scores 71 55 42 49 57 51 51 60 60 60 51 43 41 24 43 48 57 79 73 53 53 64 54 59 73 47
3
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1answer
55 views

Non-parametric version of paired t-test (Mann–Whitney U test)

I have data from 100 individuals doing a 2AFC under a control and a manipulated setting. I want to compare the means. I initially used a paired t-test. My supervisor noticed the distributions were not ...
2
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1answer
59 views
2
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1answer
43 views

If my normality test is non-significant, am I safe to use the t-test?

I took a 30 unit sample from a population. The sample distribution resulted to be normal. Can I state that the population distribution is normal too? If so, with what level of confidence?
1
vote
1answer
28 views

Paired t-test with subsamples in R?

I've been trying to find a similar "problem", but I didn't, so I'm going to try to explain what am I looking for. I have for different sites A,B,C and D. In each site I have a forest and a fallow=> ...
0
votes
1answer
30 views

t-test on seasonal effects on water quality

I am confused in the use of t-test. I monitored physical parameters of a river water two time (from the same site)- during winter and summer. Now I want to see the seasonal difference on physical ...
1
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0answers
21 views

Non parametric anova or two non parametric ttest?

I have a statistical question about a project I recently got. We performed a flow cytometry assay on 3 different groups: controls (n=5), patients before treatment (n=5) and paired patients after ...
0
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0answers
10 views

Determining dependancy of observations

I have 12 people, 6 in treatment group and 6 in control group. They gave ratings (1 to 7) to 8 different activities they were performing as a part of the experiment. I looked at another thread here ...
1
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0answers
42 views

Should I use independent samples t-test?

I need to analyse if there's a difference between poor and rich European countries (using a GDP per capita index variable) and look if it has an effect on the variable environment. The GDP per capita ...
2
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0answers
15 views

Difference test for beta–binomial variables

Let $X \sim \textrm{Beta–Binomial}(\alpha_1, \beta_1, n)$ and $Y \sim \textrm{Beta–Binomial}(\alpha_2, \beta_2, n)$ and write $\mu_1 = \frac{\alpha_1}{\alpha_1 + \beta_1}$, $\phi_1 = \alpha_1 ...
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0answers
15 views

Should I use both paired t-test and intraclass correlation coefficient to examine the interrater reliability of an instrument?

As title, I am assessing the interrater reliability of a questionnaire (actually a Barthel Index (BI)) performed by four assessors (A,B,C,D) on about 25 test subjects. I plan to examine the IRR from ...
0
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0answers
8 views

How to analyze this design? Multiple batches of Single group pre-test post-test designs

first of all - thanks for reading this. I have a want to analyze the effect of an intervention, but due to practical circumstances I cannot randomly assign people to it and the interventions differ ...
2
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3answers
56 views

Test model coefficient (regression slope) against some value

In R, when I have a (generalized) linear model (lm, glm, gls, ...
3
votes
2answers
237 views

What is the p-value for paired t-test if the two set of data are identical

As title, I have two set of data that are identical and performed paired t-test using R, the p-value for the difference estimated (which is essentially 0) is NaN. I wonder if there can be a ...
3
votes
3answers
138 views

Should I use t-test on highly skewed and discrete data?

I have samples from a highly skewed dataset about users' participation (e.g.: number of posts), that have different sizes (but not less than 200) and I want to compare their mean. For that, I'm using ...
0
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0answers
15 views

How to apply Shapiro test in R? [duplicate]

I'm pretty new to statistics and I need your help. I just installed the R software and I have no idea how to work with it. I have a small sample looking as follows: ...
3
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4answers
270 views

How exactly does null hypothesis testing work

I'm trying to gain a better understanding of how null hypothesis testing works. I have 3 questions related to the code below: Am I right in saying the probability of each t value in ...
6
votes
1answer
673 views

Should I use t-test on highly skewed data ? Scientific proof, please?

I have samples from a highly skewed (looking like an exponential distribution) dataset about users' participation (e.g.: number of posts), that have different sizes (but not less than 200) and I want ...
2
votes
2answers
27 views

Multiple comparisons with t-test: one group with different variance

If I have 3 groups that I want to compare with a t-test (correcting for multiple comparisons afterwards) but one of the groups has different variance than the other two, should I use a Welch ...
0
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0answers
6 views

MV GARCH DCC - t-test with high t-statistics

I use multivariate GARCH DCC to compute volatilities of 3 (stationary, supposedly) time series. Then I test the differences between these three volatility series with t-test and get very high ...
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0answers
9 views

Is it advisable to use t test for comparing two modules in SAP?

I have two independent samples from the maintenance and materials departments regarding the effectiveness of SAP modules. I have a likert scale data on a scale of five. Shall I use independent sample ...
2
votes
2answers
112 views

Two-Sample t-Test for Equal Means with unequal variances for large samples

How can I perform a two sample test of means with unequal variances for a very large sample in R? In case of large samples the statistic will asymptotically follow a normal distribution. Which R ...
2
votes
3answers
71 views

How do I compare sample means in this experimental-control group study?

I am hoping to compare the sample mean of an experimental group to the sample mean of three control groups. Here is some context for the study: The experimental group consists of ~60 persons with a ...
1
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1answer
102 views

$t$ test vs $\chi^{2}$ once sample is split into two groups?

I would appreciate some guidance regarding the use of a t test vs $\chi^{2}$. I am looking at some small set of demographic data (n only 13). I have divided up the sample into two sets, those with ...
1
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1answer
56 views

Paired $t$ test - Different Sample size

In testing the difference between a 'pre' survey group and 'post' survey group, I have the same sample population surveyed, yet different sample sizes (fewer respondents within the 'post' group). Am I ...
0
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0answers
24 views

Test for two confidence intervals

I would like to know if there is a test for the difference of to means m1 and m2 (continuous variables) if I have only information for mean, 2.5%- and 97.5%-quantiles. For example: $m1 \ \ \ = ...
0
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0answers
14 views

How to do mean comparison with trending data?

A client with a website has recently released a tablet app. The theory is that after installing the app a customer is less likely to log on to the website as they will use the app instead. For each ...
0
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1answer
29 views

Understanding Regression vs. Means/Median Results

I am having a little difficulty understanding my results - could someone help me understand how to interpret, and if my process is sensible? Here is an example of what I am doing I am trying to ...
0
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1answer
20 views

Is my (SPSS) independent t test correct, and how should I intrepret it?

I have a sample size of 158 students belonging to IT(N=77) and non-IT disciplines(N=81). I have carried out the independent sample t-test but I am not sure whether it's correct or not. Moreover, ...
2
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0answers
32 views

Longitudinal data where individual id is not available

I am associated with a teaching hospital, and medical students are frequently administered tests and measures to monitor their progress. I am not talking about exam results here, but of psychological ...
4
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3answers
82 views

Comparing the mean difference between data measured by different equipment, t-test suitable?

My problem is as follows: I have 2 measuring devices, both using different measuring techniques, each trying to quantify properties of objects passing their measurement area. The devices measure the ...
0
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1answer
41 views

Inconsistent x-y relationship from paired t-test and linear regression

I am analyzing an experiment comparing the effect of treatment A vs. B on the matched subject. Here are the measurements on 34 subjects: ...
2
votes
2answers
48 views

Should I perform multiple t-test or an ANOVA?

My causal comparative study seeks to three questions related to the hypothesis: a) is there a statistically significant difference between the academic achievement of 6th grade mathematics students ...
0
votes
4answers
42 views

Two groups are significantly different? Test to use

I have two groups of discrete data (integers): ...
0
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0answers
27 views

T-Tests and Regressions

my supervisor has asked me a few questions that I'm not entirely sure how to answer. For a quick summary, my study includes a small sample of 16. To describe the sample, I compared the scores of the ...
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0answers
30 views

Estimating the absolute decline of rates

Giving it another shot at describing my problem properly. I want to calculate the the crude event rates (10000person/years) for patients heart failure debut (variable name "heart_estimate") during ...
3
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0answers
35 views

Two sample differences between percentage means with negative percentages

Hello to everyone and thank you for all the help you've already unknowingly provided to me in the past. I have a group of percentages around zero that are grouped into two categories, and I wanted to ...
3
votes
1answer
22 views

Equivalent of paired $t$-test for dispersion

I'd like to compare, in a within subject design, the dispersion of two conditions. At first I thought about taking the standard deviation by individual and condition, and compute a paired $t$-test on ...
2
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0answers
69 views

Analysis for cross-subjects correlation

Suppose that an investigator has collected some longitudinal data from each of the $n$ subjects, and that a correlation coefficient is computed on the data between any pair of subjects, leading to ...
1
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1answer
28 views

Confidence Interval and Signifcance test Question

I have done the first part of the question already I just need help on the second part. You read in a U.S Census Bureau that a 99% confidence interval for the mean income in 2005 of American ...